Clinical outcomes of a twice daily metronidazole dosing strategy for Bacteroides bloodstream infections

Objective: The optimal metronidazole dose for the treatment of Bacteroides spp. has not been well-defined.

Methods: This study was a multicenter, retrospective chart review of adult patients with bacteremia secondary to Bacteroides spp. between October 2010 and March 2024. Clinical outcomes of patients who received 500mg of metronidazole twice daily were compared to those who received 500mg of metronidazole thrice daily. Clinical failure defined as a composite of 30-day recurrent infection due to Bacteroides spp. or all-cause mortality.

Results: Of the 242 patients who met the inclusion criteria, 76 received metronidazole 500mg twice daily and 166 received metronidazole 500mg thrice daily. Patients who received metronidazole twice daily did not have significantly different rates of clinical failure (15% vs 18%, P=0.561) or 30-day mortality (15% vs 17%, P=0.638) compared to those who received metronidazole thrice daily. After applying full-cohort matching, patients who received metronidazole twice daily were not at an increased risk of clinical failure [OR=0.859; 95% CI (0.283-2.606); P= 0.801] or 30-day mortality [OR = 0.897, 95% CI (0.292-2.752) P=0.8573].

Conclusions: In the largest study to date of patients with Bacteroides spp. bacteremia treated with metronidazole, twice daily dosing strategies were not associated with worse outcomes compared to thrice daily metronidazole dosing strategies.